Understanding COVID-19 Vaccines

Which COVID-19 vaccines are available in the United States? 

As of June 2022, two COVID-19 vaccines have been approved by the U.S. Food and Drug Administration (FDA), and one has been authorized for emergency use.  

Will I need a booster shot?

Studies show that protection against SARS-CoV-2 begins to decrease over time after initial vaccine doses. Additional vaccine doses (booster vaccinations) provide longer-lasting protection against COVID-19.

The FDA has authorized booster vaccinations of all three COVID-19 vaccines available in the United States. The eligibility period for a booster dose is based on several factors, including which vaccine you originally received and how long it has been since you were fully vaccinated.

Eligible people can choose which vaccine they receive as a booster dose — this is known as heterologous or “mix and match” dosing. Based on data from the National Institute of Allergy and Infectious Diseases, the FDA has determined that the benefits of mixing doses outweighs any known or potential risks.

Do the vaccines work?

Studies show that COVID-19 vaccines are very effective in preventing COVID-19, even for people at high risk for the disease.

Sometimes people who are fully vaccinated get a breakthrough infection, meaning that they test positive for SARS-CoV-2 or become ill with COVID-19. Fully vaccinated people are less likely to become seriously ill, even from COVID-19 variants.

How do I know the vaccines are safe?

Vaccines have very high safety standards, and COVID-19 vaccines are no exception. COVID-19 vaccines have undergone and will continue to undergo the most intensive safety monitoring in U.S. history.

The timeline for creating COVID-19 vaccines was shorter than for other vaccines for many reasons, including:

  • NIH scientists have been studying mRNA vaccines and coronaviruses for decades. They had a head start because they already knew a lot about how mRNA vaccines work and how to make them.

  • Researchers, the federal government, and drug companies came together like never before to cooperate and share resources, making the vaccine testing process more efficient.

  • NIH set up the COVID-19 Prevention Network (CoVPN) to coordinate existing research networks and carry out large clinical trials in tens of thousands of people efficiently. Many Americans from diverse communities volunteered to participate in the studies.

  • The FDA analyzed data from the clinical trials right away.

The safety of the authorized COVID-19 vaccines is being tracked through the Vaccine Adverse Event Reporting System, a unique safety system called v-safe that was established specifically for COVID-19 vaccines, and other systems. Vaccine manufacturers submit monthly safety updates to the FDA. The FDA also inspects vaccine production facilities and checks the quality of vaccine batches.

The Journey of a Vaccine

Learn about the four phases of clinical research, what questions researchers try to answer in each, and how a vaccine is developed, approved, and manufactured.

Do the vaccines protect against virus variants? 

Studies and current data show that the antibodies our bodies make after vaccination recognize and protect against COVID-19 variants. This is being closely investigated, and more studies are underway.  

The rise of these variants is a reminder that as long as SARS-CoV-2 continues to spread, it has the potential to evolve into new variants. Widespread vaccination will help reduce the rise of additional variants. 

Can children get  a vaccine? 

Children and teens age 6 months and older can now get the Pfizer and Moderna COVID-19 vaccines. Eligible children age 5 and older can also receive a booster dose of the Pfizer vaccine.

Do the vaccines have any side effects?

All vaccines may cause some side effects, which are normal signs that your body is making antibodies. These side effects go away in a few days. Many people have no side effects. 

Serious side effects that could cause long-term health problems are extremely unlikely following any vaccination, including COVID-19 vaccination. These rare side effects usually appear within six weeks of receiving a vaccine dose. If you have any health problems after vaccination, report them to the Vaccine Adverse Event Reporting System (VAERS).

Rare cases of heart inflammation have been reported after mRNA COVID-19 vaccination, mainly in male adolescents and young adults.

The CDC continues to recommend vaccination for everyone 5 years of age and older, given the greater risk of serious complications related to COVID-19.

How COVID-19 Affects Pregnancy

Should you get the vaccine during pregnancy? Does the vaccine cause infertility? NIH research is helping to answer these questions and more.

How do I get a COVID-19 vaccine?

The federal government is providing FDA-authorized COVID-19 vaccines free to all people living in the United States, regardless of their immigration or health insurance status. Search vaccines.gov, text your ZIP code to 438829, or call 1-800-232-0233 to find COVID-19 vaccine locations near you. Contact your state health department to find additional vaccination locations in your area. 

If you have difficulty reaching a vaccination site, you may be able to get an in-home vaccination. Check a list of services that may offer in-home COVID-19 vaccinations in your area.

Should I get a vaccine if I've had COVID-19 in the past?

Studies indicate that vaccination produces a stronger immune response than the one produced by COVID-19 infection. The benefits of vaccination after infection far outweigh any known or potential risks.

To ensure that people who recover from COVID-19 are protected from getting the disease again, the CDC recommends that they get vaccinated. The timing of vaccination depends on when a person had COVID-19 and whether and when they received treatment. If you have had COVID-19 and want to be vaccinated, talk to your doctor about when you should get the vaccine. 

Are vaccines still being researched?  

New and ongoing studies on vaccines are underway. NIH Institutes and Centers, in partnership with private businesses, continue to study different types of vaccines. 

Some current research aims to determine whether approved vaccines will grant immunity against emerging COVID-19 variants and whether new vaccines will be needed. Other vaccine studies continue to monitor the health of people who have already had a vaccine to determine their effectiveness over a longer period of time. 

NIH has begun a clinical trial to assess the antibody response to an extra dose of an authorized or approved COVID-19 vaccine in people with autoimmune disease who did not respond to an original COVID-19 vaccine regimen. The trial also will investigate whether pausing immunosuppressive therapy for autoimmune disease could improve the antibody response for people who are receiving that additional vaccine dose.

COVID-19 Vaccine Resources

HHS shares information about the vaccine distribution process.

The CDC shares information to answer common questions about vaccine safety.

Learn what to expect when you volunteer for a vaccine clinical trial.

Get the facts about COVID-19 vaccine studies.

Page last updated: June 21, 2022